A guard known as a "duraguard" is utilized with a small rotating cutting tool in brain surgery to move the dura layer away from the inner skull surface as the cutting tool is moved to cut an opening in the skull. The guard consists of an arm fixed at one end to the cutting tool housing and having a foot at the outer end which covers and is spaced slightly from the end of the cutting tool. The foot enters between the skull and the dura and serves to move the dura away from the inner skull surface should it be stuck to the skull surface, thereby preventing the tool from cutting anything but the skull itself. During the skull cutting operation, the arm follows in the cut made by the tool and the foot projects slightly ahead of the outer tip of the cutting tool. With the arm and foot fixed to the end of the housing and fixed relative to the axis of the cutting tool extending from the end of the housing, it is difficult to cut curved lines or corners with the instrument since the arm of the guard wants to follow directly to the location of the cutting tool. Thus, when the cutting tool executes a sharp curve, the arm wants to cut across the curved portion between the arm and the cutting tool. Therefore, it is necessary to rotate the tool housing while moving the cutting tool in order for the arm to follow in the curved slot already cut in the skull by the cutting tool. When the fixed duraguard is used to cut a complete round opening, it requires the switching of hands on the tool in order to move the tool in different directions and keep the duraguard following as well as possible.
Since the arm is required to follow through the slit in the skull, the foot and arm can be forced against the blade and thereby damage to both the blade and the guard can occur. After the duraguard arm is bent, it is hard to align since the end of the duraguard must be opposite the cutting tool at all times and it is usually necessary to return the complete cutting tool to the factory for replacement of the guard. There have been attempts made to produce swiveling duraguards which rotate on the end of the cutting tool housing but no device has been produced which removes the tendency of the foot to move against the blade and when this happens, the duraguard will get cut up by the blade or generates heat which is undesirable during the cutting operation.